1. Field of the Invention
The present invention relates to Local Area Networks (LANs) in general and, in particular, to improved concentrators and stations for use in said LANs.
2. Prior Art
The use of switches for interconnecting LAN segments are well known in the prior art. ALAN segment may be defined as a group of stations connected to a common media. By interconnecting LAN segments through a switch, simultaneous communication between groups of stations are made possible and, as a consequence, the bandwidth capabilities of the interconnected LANs are increased.
U.S. Pat. No. 5,274,631 describes a switching system for interconnecting ethernet LAN segments. The switching system consists of a multiplex switching logic module to which a plurality of packet processors are connected. Each packet processor is associated with a port to which an ethernet LAN segment is connected. The packet processor routes frames through the switch, from a station on one LAN to another station on another LAN.
There has been a steady demand for more bandwidth in such systems. The demand, in part, is based upon growth in the number of network stations and the increase processing power of such stations allowing them to use the growing number of data intensive applications such as multimedia applications.
Another phenomenon pushing the need for increased bandwidth is the trend to centralize server functions. One could envision a network in which one server services several different LAN segments. A straightforward way of providing the high bandwidth required to enable such a server to serve multiple LAN segments would be to use a full-duplex link and devices for coupling the server and the LAN segments. The use of true full-duplex links in non-LAN communications networks are well known. However, there are several problems to overcome in adapting full-duplex to LAN systems.
U.S. Pat. No. 5,155,726 describes a technique for establishing and maintaining full-duplex between two stations on a token ting network. Each station enters the ring operating in a token (half-duplex) mode. Each station then ascertains if only one other active station is operating on the token ring network and, if so, exchanges frames with the other station to establish full-duplex communication.
Even though the patent is a step in the right direction, it has certain drawbacks. The duplex operation is between two stations on a token ring LAN segment. Each station must enter the ring in half-duplex (token) mode of operation and then switch to full-duplex if network conditions warrant the switch. This calls for an expensive station adapter since both token (half-duplex) MAC and full-duplex MAC must be implemented. In addition, the patent cannot be used with a switch.